Yangon  - United Nations special human rights envoy Tomas Ojea Quintana visited Myanmar's junta headquarters of Naypyitaw Wednesday, for talks likely to concentrate on the country's estimated 2,100 political prisoners.

UN officials said it was not known which generals Quintana would meet in Naypyitaw, 350 kilometres north of Yangon. He is expected to at least meet with Prime Minister General Thein Sein, who also met with UN special envoy Ibrahim Gambari on an official visit last month.

Myanmar's military supremo and junta chief, Senior General Than Shwe, has refused meetings with any UN representatives since May, when he granted an audience with UN Secretary General Ban Ki-moon.

Quintana arrived in Yangon on Saturday for a trip aimed at pressing for the freedom of the country's 2,100 political prisoners, including opposition leaders Aung San Suu Kyi and Tin Oo.

Tin Oo, the 82-year-old deputy leader of the opposition National League for Democracy (NLD), was sentenced to another year under house arrest on the eve of Quintana's arrival.

The UN rapporteur on human rights also visited jails in the Karen State and the notorious Insein prison in Yangon, meeting with several political prisoners.

Critics of his visit called it a "showboat" mission for the junta, permitted only to improve its image at the 14th summit of the Association of South-East Asian Nations in Thailand later this month.

While allowing the visit, the regime has already sent a clear message to Quintana that it will continue to brook no political opposition.

Besides slapping another year on to Tin Oo's house arrest Friday, the day before Quintana's arrival, Myanmar courts sentenced NLD members Nyi Bu and Tin Min Htut to 15 years for sending an open letter to the UN in August that was critical of the military's plans to set up a civilian government.

Quintana hopes to persuade the junta to free hundreds of political prisoners before a scheduled general election in 2010.

His mission was to encourage the regime to progressively release "prisoners of conscience," giving independence to the judiciary, bringing laws into line with international human rights standards and training officials to respect these rights, according to a statement released by the UN in Geneva.

It was not known if he would visit Suu Kyi, who has been under house arrest since May 2003 and has spent almost 13 of the past 19 years in detention. (dpa)